A puffer type circuit breaker is generally provided with a gas compressor comprising a piston and a cylinder which is slidable relative to the piston, and with an insulating nozzle for effectively blowing an arc-extinguishing gas of high pressure obtained by means of the gas compressor onto an arc which may be generated when the contactors of the circuit breaker are separated from each others.
FIG. 8 shows an example of the puffer type circuit breakers of such type.
In FIG. 8, breaking portions enclosed within the circumference of an arc-extinguishing gas is shown and in this portion a gas compressor 8 is composed of a puffer cylinder 1 integrally formed with a shaft 6 connected to a not-shown operating device, and of a stationary piston 7 slidably engaging with the cylinder 1. A movable contactor 2 is mounted on the shaft 6, and an insulating nozzle 4 and an insulation cover 3 are secured to the puffer cylinder 1 by surrounding the movable contactor 2. The insulating nozzle 4 is formed with a single throat portion 4a corresponding to a nozzle through which a fixed contactor 11 is inserted, and the fixed contactor 11 is adapted to contact with the movable contactor 2. The fixed contactor 11 is adapted to contact with the movable contactor 2. The fixed contactor 11 has a larger diameter portion 11b of diameter D.sub.2 on the base side thereof. In the closing state of the breaker, as shown in FIG. 8, the smaller diameter portion 11a of diameter D.sub.1 on the tip thereof. In the closing state of the breaker, as shown in the FIG. 8, the larger diameter portion 11b is inserted at the distance X.sub.1 from the throat portion 4a to the shown position. The throat portion 4a has an inner diameter D.sub.A slightly greater than the outer diameter D.sub.2 of the larger diameter portion 11b.
When the shaft 6 is moved to the right direction by means of a not-shown operating device, the arc-extinguishing gas in the gas compressor 8 is compressed. In an initial stage of the compression, exhaust ports 10 of the shaft 6 for opening the central hollow portion of the shaft 6 to environment are closed by a closing member 7a occuring at the mounting base portion of the stationary piston 7, and the throat portion 4a of the insulating nozzle 4 is closed by the larger diameter portion 11b of the fixed contactor 11. After that, as disclosed in Japanese Patent Publication No. 56-12973 corresponding to U.S. Pat. No. 3,839,613, gas flows 21 and 22 passing through the hollow portion of the shaft 6 take place as shown in FIG. 9, and when the throat portion 4a is moved by a distance X.sub.1 so as to reach the smaller diameter portion 11a as disclosed in Japanese Patent Publication No. 58-26133, gas flows 25 and 26 passing through the throat portion 4a take place also as shown in FIG. 9, thereby allowing the arc which has been generated by separating both contactors 2 and 11 from each other to be extinguished by blowing those gas flows.
However, the breaking ability of small capacitive current is noted to the effect that at the time when the distance between the both contactors 2 and 11 is relatively small, an electric current is broken, and after that, a high voltage is generated between the contactors. In FIG. 8, after the throat portion 4a is moved so as to go through the larger diameter portion 11b of the fixed contactor 11, a gas flow take place so as to discharge a gas through the gas between the throat portion 4a and the smaller diameter portion 11a, thereby allowing the gas pressure in the neighborhood of the tip of the fixed contactor 11 to be lowered. Accordingly, a dielectric strength between the facing portions of both contactors 2 and 11 are deteriorated to lower the breaking ability of small capacitive current.
In connection with the abovementioned matters, a puffer type circuit breaker disclosed in Japanese Patent Application Laid-Open No. 59-103238 is shown in FIG. 10. The members and portions corresponding to those shown in FIG. 8 are denoted with the same reference numbers. The only differences between the apparatuses shown in FIGS. 8 and 10 will be described as follows.
In the fixed contactor 11, a blocking plate such as a disk is mounted on the base portion thereof, and a second throat portion is defined by the blocking plate 4 and the inner surface of a straight cylindrical portion 4b formed in the downstream portion of the insulating nozzle 4.
In this structure, since it prevents the reduction of the gas pressure on the tip of the fixed contactor 11 to provide with the blocking plate 9, it is intended to improve the breaking ability of small capacitive current in such manner as to generate a high voltage between both contactors when the distance between both contactors 2 and 11 is not fully provided by separation of those contactors.
In this puffer type circuit breaker, however, the inner diameter of the first throat portion 4a formed in the upstream side of a blowing gas is equal to the outer diameter of the fixed contactor 11. Therefore, when the blocking plate 9 is moving along the inner surface of the straight cylindrical portion 4b in the insulating nozzle 4 as the both contactors 2 and 11 are separated from each other, the volume of a chamber defined by the fixed contactor 11 and the blocking plate 9 increases rapidly, thereby allowing the chamber to be under a negative pressure. Thus, the tip of the fixed contactor 11 passes through the first throat portion 4a, and the arc-extinguishing gas rapidly flows into the negative-pressured chamber as abovementioned via the tip of the fixed contactor 11 from the gas compressor 8. In this manner, since the pressure or density of the gas on the tip of the fixed contactor 11 is lowered, it is impossible to improve the breaking ability of small capacitive current.